Terephthalic acid is a monomer
used to produce polyethylene terephthalate.The main commercial route to
terephthalic acid is the partial oxidation of p-xylene in acetic acid as a solvent
at approximately 200 °C and 15-30 atm with a combination of manganese,
bromine, and cobalt as catalyst. Recent studies have considered the use of high
temperature water (HTW) as a solvent instead of acetic acid as it is more
environmentally benign. The synthesis of terephthalic acid has been carried out
in water in both sub critical and supercritical conditions. The yields of
terephthalic acid and other products have been studied in a catalytic
environment using MnBr2 as the catalyst and hydrogen peroxide as the
oxidant. The variation in the yield of terephthalic acid has been studied by
varying factors like temperature, batch holding time, catalyst concentration,
oxidant concentration and initial p-xylene concentration.The highest yield
obtained was 49 ± 8 % at 300oC using MnBr2 as the
catalyst and hydrogen peroxide as the oxidant. The hydrothermal stability of
terephthalic acid in high temperature was also evaluated. Benzoic acid was the
most stable product of decarboxylation and showed negligible degradation.A decarboxylation pathway was also
established and the various parameters involved in the rate equation were
fitted according to experimental data. Finally an economic and environmental
assessment of the HTW based process was done in order to study the feasibility
of p-xylene oxidation as a continuous process. With a capital investment nearly
equal to the traditional acetic acid based process coupled with reduced
emissions this method seems to have a promising future.